LTE is a fully packetized 4G air interface for cellular communication. An eNodeB is the cell base station of an LTE wireless communication network. A source eNodeB is an eNodeB serving as an LTE access point for a user equipment. User equipment may be a smart phone, tablet, personal computer, or any processing device with an LTE transceiver. A neighbor eNodeB is an eNodeB that sends LTE signals that are received by a user equipment that has a different source eNodeB. A source eNodeB may decide on a handover of a user equipment to a target eNodeB that the source eNodeB selects.
The decision to initiate a handover is made by identifying a neighbor eNodeB that has a stronger signal than the source eNodeB. The source eNodeB delegates to user equipment the measuring of strength of signals sent from neighbors. The source eNodeB accomplishes this delegation of measurement in two steps. First the source eNodeB sends the user equipment a measurement control message. This message has threshold conditions that tell the user equipment when to upload signal strength measurements. The user equipment repeatedly measures the strength of signals sent from source eNodeB and neighbor eNodeBs. When the user equipment detects that a signal strength measurement crosses a threshold condition, the user equipment sends to the source eNodeB a measurement report that bears strength measurements of signals sent from eNodeBs.
The source eNodeB receives and analyzes the measurement report to decide whether to handover the user equipment to another eNodeB. The source eNodeB also analyzes the measurement report to select which neighbor eNodeB should be the target of the handover. It is suboptimal to select a target eNodeB based solely on measurement reports. This is likely to saturate some eNodeBs and underutilize others. For example a well-placed eNodeB with line of sight to many user equipment may be selected too often as the target of a handover. The well-placed eNodeB would become saturated with many user equipment. To help with load balancing a source eNodeB should consider how loaded are neighbor eNodeBs.
There may be several ways and dimensions for measuring how loaded is a neighbor eNodeB. The load on an eNodeB may determine outcomes such as voice quality or handover success. For example during a handover a target eNodeB needs a spare contention-free preamble to assign to the arriving user equipment. If the target eNodeB is saturated and lacks a spare contention-free preamble, then the user equipment must use a contention-based preamble as a fallback tactic. This fallback tactic is slower and less reliable, so the handover is more likely to fail or cause a brief audible aberration. A source eNodeB that ignores the preamble usage of its neighbors might be less able to balance load within the cellular network. This may jeopardize the quality of service of a voice call being handed over to a saturated target eNodeB.